Microbiology Chapter 6

Prions are of significance because they cause infections of A. domestic animals and humans. B. plants. C. fungi. D. prokaryotes.

A. domestic animals and humans.

Viroids are of economic significance because they cause disease in A. plants. B. animals. C. humans. D. all of the choices

A. plants.

Most enveloped viruses use the host __________ membrane as their envelope source. A. plasma B. nuclear C. mitochondrial D. none of these

A. plasma

Hemagglutination is A. the clumping together of red blood cells in the presence of a viral suspension. B. the binding of iron in the process of a viral suspension. C. the clumping together of infected cells in the presence of a viral suspension. D. none of the choices

A. the clumping together of red blood cells in the presence of a viral suspension.

Virion size ranges from A. 1-40 nm. B. 10-400 nm. C. 600- 1,000 nm. D. 1,000-10,000 nm.

B. 10-400 nm.

0.2 mls of a 10-4 dilution of a virus preparation yields 90 plaques. What is the number of PFU per ml in the undiluted virus preparation? A. 9.0 105 B. 4.5 106 C. 4.5 107 D. 9.0 108

B. 4.5 106

Which of the following has been associated with a form of liver cancer? A. Human papilloma virus. B. Hepatitis B virus. C. Human T-cell lymphotropic virus. D. Hepatitis A virus.

B. Hepatitis B virus.

Which of the following is most true of a viral DNA genome? A. It uses the same four nitrogenous bases found in prokaryotic and eukaryotic DNA. B. It may have the normal bases found in prokaryotic and eukaryotic DNA, or it may have one or more unusual bases. C. It is usually composed of unusual bases unique to viruses. D. Viruses do not use DNA for their genome.

B. It may have the normal bases found in prokaryotic and eukaryotic DNA, or it may have one or more unusual bases.

Which is not true of viruses? A. They can exist in an intracellular or extracellular phase. B. They infect animal and plant cells only. C. They can be observed with an electron microscope. D. They are acellular. E. They replicate only inside host cells.

B. They infect animal and plant cells only.

Some complex viruses have icosahedral symmetry in the head region and helical symmetry in the tail. Overall, these viruses are said to have __________ symmetry. A. bilateral B. binal C. complex D. none of these

B. binal

The protein coat surrounding the viral genome is called the A. capsule. B. capsid. C. matrix. D. envelope.

B. capsid.

Human cancer causing viruses most often have a ___________ genome. A. ssDNA B. dsDNA C. ssRNA D. dsRNA

B. dsDNA

Nonenveloped viruses most often gain access to eukaryotic host cells by A. fusion with the host cell plasma membrane followed by entrance of the nucleocapsid into the cytoplasm. B. endocytosis. C. pinocytosis. D. nucleic acid injection through the plasma membrane.

B. endocytosis.

Glycoprotein spikes protruding from the outer surface of viral envelopes function as A. toxins. B. factors that bind to host cells. C. cell lysis factors. D. factors needed for site specific recombination.

B. factors that bind to host cells.

Two major types of symmetry found in viruses include A. icosahedral and radial. B. icosahedral and helical. C. helical and radial. D. radial and bilateral.

B. icosahedral and helical.

In an enveloped virus, the part of the virus including the nucleic acid genome and the surrounding protein coat but not the envelope is called the A. capsid. B. nucleocapsid. C. matrix. D. virion.

B. nucleocapsid.

Adult T-cell leukemia is thought to be caused by A. herpesviruses. B. retroviruses. C. parvoviruses. D. picornaviruses.

B. retroviruses.

A __________ genome exists as several separate, nonidentical molecules that may be packaged together or separately. A. diploid B. segmented C. polyploid D. fractionated

B. segmented

Viral capsids are generally constructed without any outside aid once the subunits have been synthesized. This process is called A. facilitated assembly. B. self-assembly. C. spontaneous maturation. D. self-maturation.

B. self-assembly.

The simplest viruses consist of A. RNA only. B. Protein only. C. RNA or DNA in a protein coat. D. RNA or DNA in a protein coat covered with lipid envelope. E. RNA, DNA and enzymes in a protein coat with a lipid envelope.

C. RNA or DNA in a protein coat.

Which of the following is/are not true about viral envelopes? A. The envelope proteins are virus specific. B. The envelope lipids and carbohydrates are derived from the host. C. They are typical lipid monolayers with embedded viral proteins. D. The envelope proteins are virus specific and the envelope lipids and carbohydrates are derived from the host

C. They are typical lipid monolayers with embedded viral proteins.

Which of the following is true of viruses in the extracellular phase? A. They possess many different enzymes. B. They can reproduce independently of living cells but only at a slow rate. C. They behave as a macromolecular complex and are no more alive than are ribosomes. D. They possess many different enzymes and they can reproduce independently of living cells but only at a slow rate

C. They behave as a macromolecular complex and are no more alive than are ribosomes.

Which of the following is not a mechanism by which viruses cause cancer? A. They carry a cancer-causing gene into the cell. B. They encode proteins that bind to and inactivate host cell proteins known as tumor suppressor proteins. C. They produce defective interfering particles. D. An expression of viral proteins results in abnormal expression of genes that regulate cell growth and reproduction.

C. They produce defective interfering particles.

The nucleic acids carried by viruses usually consist of A. DNA. B. RNA. C. either DNA or RNA. D. both DNA and RNA simultaneously.

C. either DNA or RNA.

Poliovirus receptors are found A. in cells of all tissues. B. in spinal cord anterior horn cells only. C. in nasopharynx, gut, and spinal cord anterior horn cells. D. in gut cells only.

C. in nasopharynx, gut, and spinal cord anterior horn cells.

Many of the enzymes found in virus particles are A. required for viral attachment to host cells. B. involved in viral entry into host cells. C. involved in the replication of viral nucleic acid. D. all of the choices

C. involved in the replication of viral nucleic acid.

Genes whose expression (or abnormal expression) causes cancer are called A. cancer genes. B. progenies. C. oncogenes. D. carcinogens.

C. oncogenes.

A ________ assay is most useful for determining the viability of a viral preparation? A. direct (electron microscopic) count B. hemagglutination C. plaque D. PCR

C. plaque

Viral capsid protein subunits are called A. auxomers. B. elastomers. C. protomers. D. viromers.

C. protomers.

A complete virus particle is called a A. capsid. B. nucleocapsid. C. virion. D. cell.

C. virion.

Which of the following diseases is (are) caused by prions? A. Scrapie. B. Mad cow disease. C. Kuru and Creutzfeldt-Jakob Disease. D. All of the choices.

D. All of the choices.

Which of the following is not true regarding the human hepatitis D virusoid? A. Its genome is a circular, single-stranded RNA molecule. B. It needs a helper virus to infect host cells. C. It produces one protein called the delta antigen. D. All of the statements are true.

D. All of the statements are true.

Which of the following can be used to cultivate plant viruses? A. Cultures of separated plant cells. B. Whole plants. C. Plant protoplast cultures. D. All of these can be used to cultivate plant viruses.

D. All of these can be used to cultivate plant viruses.

Which of the following is not true of viroids? A. Viroids are small circular ssRNA molecules. B. Viroids have no protein capsids. C. Viroid RNA does not serve as mRNA nor does it direct the synthesis of mRNA. D. Extracellular viroids have a lipid bilayer envelope.

D. Extracellular viroids have a lipid bilayer envelope.

Which of the following represent(s) the way(s) in which enveloped viruses acquire their envelopes? A. Budding through the plasma membrane. B. Budding through internal cellular membranes. C. Viral enzymes are responsible for production of the envelope. D. For some viruses, a is correct; for other viruses, b is correct.

D. For some viruses, a is correct; for other viruses, b is correct.

Which of the following is not true of viruses? A. Viruses are acellular. B. Viruses consist of one or more molecules of DNA or RNA enclosed in a coat of protein and sometimes in other more complex layers. C. Viruses can exist in two phases: intracellular and extracellular. D. Viruses replicate by binary fission.

D. Viruses replicate by binary fission.

Animal viruses have been cultivated in A. suitable host animals. B. embryonated eggs. C. tissue cultures (monolayers of animal cells). D. all of the choices

D. all of the choices

Viral envelopes are composed of A. proteins. B. lipids. C. carbohydrates. D. all of the choices

D. all of the choices

Virus morphology does not include which of the following characteristics? A. size B. shape C. presence or absence of an envelope D. host range

D. host range

The function of the viral protein coat is to A. protect the viral genetic material. B. aid in the transfer of the viral genetic material between host cells. C. elicit the production of protective antibodies. D. protect the viral genetic material and aid in the transfer of the viral genetic material between host cells.

D. protect the viral genetic material and aid in the transfer of the viral genetic material between host cells

In which of the following stages of the viral infectious cycle do enveloped viruses usually acquire their envelopes? A. penetration B. component biosynthesis C. assembly D. release

D. release

Viroids are: A. proteins that may infect man and other animals causing spongiform encephalopathy. B. a class of so-called slow viruses. C. a new class of small single stranded DNA viruses that infect some animals. D. short infectious single stranded RNAs that can infect some plants.

D. short infectious single stranded RNAs that can infect some plants.

Bacterial viruses are so named because they have prokaryotic cell structures similar to their bacterial hosts.

FALSE

In a plaque assay, the number of infectious virions is usually identical to the number of virus particles present.

FALSE

Like bacteria and eukaryotic microorganisms, most viruses can be cultured using artificial media.

FALSE

The presence or absence of an envelope is not useful in classifying viruses because any given virus may at one time have an envelope and at another time not have an envelope.

FALSE

There are no known human diseases that have been linked to prions.

FALSE

Viruses have typical cellular structure like other living organisms.

FALSE

Viruses infecting protists, including algae, have never been detected.

FALSE

__________ are glycoprotein spikes protruding from the outer surface of the viral envelope.

Peplomers

Almost all known plant viruses are RNA viruses.

TRUE

Available evidence is consistent with the proposal that prion diseases are caused by infectious proteins.

TRUE

Enveloped viruses may enter their host cells by engulfment within coated vesicles (endocytosis).

TRUE

Enveloped viruses may enter their host cells by fusion of their envelope with the cytoplasmic membrane, thereby depositing their nucleocapsid within the cell.

TRUE

One way in which small viruses package more information into a very small genome is to use overlapping genes so that the same base sequence is read in more than one reading frame.

TRUE

Prions consist of proteins and have no apparent nucleic acid genome.

TRUE

The largest of the viruses are similar in size to some small bacteria and are large enough to be seen with a light microscope.

TRUE

The mechanism of pathogenesis by prions may involve a conformational change in the prion protein (PrP) to an abnormal form.

TRUE

The most common capsid morphologies are icosahedral and helical.

TRUE

Virus receptors are often not distributed uniformly over the surface of host cells, but are instead concentrated in lipid rafts.

TRUE

Viruses in the extracellular state possess few, if any, active enzymes.

TRUE

Viruses such as MS2 and Qß pack additional information into their genomes through the use of overlapping genes.

TRUE

cosahedral viruses are constructed from ring- or knob-shaped units called __________.

capsomers

Microscopic or macroscopic degenerative changes or abnormalities in infected host cells and tissues are called __________ __________.

cytopathic effects

Viruses that are polyhedrons with 20 sides are said to have __________ symmetry.

icosahedral

Localized areas of destruction occurring on plants that have been infected by a virus are referred to as __________ lesions.

necrotic

Some viruses cause abnormal growth of cells rather than destruction. This is called __________.

transformation